Our aim in Project I is to develop our theoretical perspective on the "practical phonology", that is, on phonological structures of public language use. The research complements work on neurobiological foundations on speech in Project II and will inform on reading about the fundamental elements of the spoken language that readers access. A central requirement of phonological language is that communicators typically achieve "parity," a relation of sufficient equivalence between messages sent and received. Without this requirement, language use would not serve to communicate. Because language is an evolved system, parity achievement will have been selected for, and therefore, phonological systems will foster achievement of parity. A parity fostering system is one in which components of the language that serve to make a speaker's message public, that is, phonological elements, are themselves public things. In addition, they are elements of the message through all phases of an exchange; they are elements of the phonological message as planned by the speaker, as implemented in the vocal tract and as perceived. We propose that gestures (linguistically significant actions of the vocal tract) are the phonological primitives that are preserved in every phase of a spoken communicative event. Our research is designed to test and further develop these ideas. We propose to develop our theory of phonological competence, Articulatory Phonology, by showing that it can insightfully address the kinds of phonological systematicities that serve as test cases for phonological theories. Next we show that the primaries of Articulatory Phonology, gestures, are also units of encoding in utterance planning and production. Third, we attempt to show that gestures are the primitive of perceived phonological structure. Our final lines of research address two central functions of phonological structures in a practical phonology. One is lexical specification; phonological elements must uniquely identify words, distinguishing them from others. We propose to determine how phonological structure interacts with lexical knowledge in speech perception. The second function is social identification. People mark their social affiliations by their particular phonetic implementations of phonological structures. We propose to study "gestural drift", the drift of speakers toward the gestural dialect of the ambient speech community.